As shown in FIG. 1, a heat treatment apparatus, which is usually used in heat treating workpieces, typically comprises: a main body 10, made of refractory material and equipped with a pair of openings 11 through which a workpiece 1 is introduced into and discharged out of the apparatus; opening shutter units 20, mounted on the main body 10 to close and open the openings 11; an internal opening shutter unit 30, openably mounted on the main body 10 so as to divide the interior space of the main body 10 into a heating chamber 12 and a cooling chamber 13 and having a passage hole H which allows communication between the heating chamber 12 and the cooling chamber 13 in a closed condition; a transfer unit 40, to transfer the workpiece 1, which is introduced through the opening 11, to the heating chamber 12 and the cooling chamber 13 and then discharge the workpiece 1 outside through the second opening 11; a heating unit 50 provided in the heating chamber 12 to heat the workpiece 1; a cooling unit 60 provided in the cooling chamber 13 to cool the workpiece 1; a temperature sensor 70 provided on the heating chamber 12 to measure the internal temperature of the heating chamber 12; and a control unit 80 intended to receive an output signal from the temperature sensor 70 and to control the heating unit 50 in response to the output signal, and further to control operations of the opening shutter units 20, the internal opening shutter unit 30 and the transfer unit 40.
The pair of openings 11 is provided in respective opposite sides of the main body 10 to allow access to the heating chamber 12 and the cooling chamber 13, so that the workpiece 1 can be introduced into the heating chamber 12 through one of the openings 11 and can be discharged from the cooling chamber 13 through the other of the openings 11.
The opening shutter unit 20 is comprised of a door panel 21 mounted on the main body 10, and an actuator 22 connected to the door panel 21 and driven in response to a signal from the control unit 80. In other words, the opening shutter unit 20 is configured so as to operate the door panel 21 in response to the signal from the control unit 80, thus opening or closing the opening 11.
The internal opening shutter unit 30 is comprised of a partition panel 31, which is vertically provided in the main body 10 to be raised and lowered, and an actuator 32, which is connected to the partition panel 31 and driven in response to a signal from the control unit 80. Consequently, through a raising or lowering movement of the partition panel 31 by the actuator 32, the heating chamber 12 and the cooling chamber 13 are communicated with each other or are blocked from each other.
The transfer unit 40 is largely comprised of conveying rollers, which are internally disposed on the bottom of the main body 10 and driven by a drive motor (not shown), the heating unit 50 is largely comprised of an electric heater, and the cooling unit is largely comprised of an oil cooling type of cooling apparatus comprised of a cooling oil tank provided at a lower position of the cooling chamber 13 and storing a cooling agent therein, and an elevating apparatus 62 intended to lower and raise the workpiece 1, transferred into the cooling chamber 13, thus immersing the workpiece 1 in the cooling agent.
Consequently, according to a heating sequence, which has been previously programmed, the control unit 80 controls the opening shutter units 20, the internal opening shutter unit 30, the transfer unit 40 and the heating unit 50 such that the workpiece 1, which is introduced into the heating chamber 12, is heated to a predetermined temperature, and is transferred into the cooling chamber 13, in which the workpiece is cooled, thus completing the heat treatment. In this regard, the control unit 80 controls the heating unit 50, according to the internal temperature of the heating chamber 12, which is measured by the temperature sensor 70, thus maintaining the internal temperature of the heating chamber 12 constant.
In this heat treatment apparatus, when air is introduced into the apparatus during the heat treatment, oxygen in the air reacts with the workpiece 1, thus forming an oxide film on the workpiece or deteriorating the inherent physical properties of the workpiece 1.
To overcome this problem, a proper kind of ambient gas is supplied into the heating chamber using an ambient gas supply apparatus 90 connected to the heating chamber 12, thus preventing the introduction of oxygen and securing consistent quality of the heat-treated workpiece 1.
The ambient gas is largely comprised of Rx gas, which is produced by mixing hydrocarbon-based gas, such as natural gas, propane gas, butane gas and the like with air in respective adequate amounts and passing the mixture through a reaction catalyst heated to a temperature of 100-1100° C. The gas supply apparatus 90 is connected to the heating chamber 12 via an ambient gas feed pipe 91 so as to supply ambient gas into the heating chamber 12. A feed pipe 92 is connected to the ambient gas supply apparatus 90 to supply hydrocarbon-based gas and air thereto. The ambient gas feed pipe 91 is provided with an intake valve 91a so as to control the amount of ambient gas supplied through the ambient gas feed pipe 91.
The heating chamber 12 further includes an analyzer 100 for analyzing the composition of the ambient gas in the heating chamber 12, a supplemental gas supply unit 110 for additionally supplying hydrocarbon-based gas and air to the heating chamber 12, a fan 120 and the like. The supplemental gas supply unit 110 comprises a hydrocarbon-based gas feed pipe 111, an air feed pipe 112, and control valves 111a and 112a, which are provided on intermediated portions of the gas feed pipe 111 and the air feed pipe 112, respectively.
As a result, when adequate amounts of hydrocarbon-based gas and air are supplied to the heating chamber 12 by controlling the control valves 111a and 112a depending on the composition ratio, analyzed using the analytical instrument, the hydrocarbon-based gas and the air are mixed with each other in the heating chamber 12 and react with each other due to the high internal temperature of the heating chamber 12, thus generating the ambient gas. This therefore enables the control of the composition ratio of the ambient gas.
The partition panel 31 of the internal opening shutter unit 30 includes the passage hole H formed therein, which allows the heating chamber 12 and the cooling chamber 13 to be communicated with each other. The cooling chamber 13 is provided with an exhaust pipe 131. Consequently, the ambient gas, which is supplied in the heating chamber 12, is introduced into the cooling chamber 13 through the passage hole H or the opening defined by the opened partition panel 31 of the internal opening shutter unit 30, and is then discharged outside through the exhaust pipe 131. In this arrangement, the passage hole H is provided by forming a through-hole in the lower part of the partition panel 31.
Therefore, when an amount of ambient gas sufficient to maintain the internal pressure of the heating chamber 12 higher than atmospheric pressure is supplied into the heating chamber 12, the ambient gas is also introduced into the cooling chamber 13, thus blocking the introduction of external air thereinto. As a result, it is possible to prevent the heated workpiece 1 from contacting the external air, thus enhancing the quality of the heat-treated workpiece 1.
Meanwhile, because the ambient gas is combustible and toxic gas, if the ambient gas is discharged outside without any treatment, it causes undesirable accidents such as gas poisoning, fires, explosions and the like. To avoid the problem, the waste ambient gas, which is discharged through the exhaust pipe 131, is completely burned in a first combustor 130 connected to the exhaust pipe 131, and is then discharged into the atmosphere. Furthermore, because there is a possibility of ambient gas leaking from the heat treatment apparatus at the time of opening of the openings 11, a pair of second combustors 140, which is connected to the control unit 80, is externally mounted under the openings 11 of the heating chamber 12 and the cooling chamber 13, respectively. Consequently, when the opening is opened by actuation of the opening shutter unit 20, the second combustor 140 is activated to thus burn the ambient gas discharged through the opening 11, thus reliably preventing the ambient gas from being discharged outside. In addition, when the second combustor 140 is activated, a flame-proof curtain is formed outside the opening 11, so that the ambient gas in the main body 10 and the external air cannot be mixed with each other, thus efficiently preventing the ambient gas from leaking outside.
In this heat treatment apparatus, the internal temperature may vary due to the workpiece introduced into the main body, or the internal pressure of the heating chamber 12 and the cooling chamber 13 may be varied by the openings in the opening shutter units 20 and the internal opening shutter unit 30. When the internal pressure is lowered in this way, external air may be introduced into the main body. In particular, if the internal pressure of the cooling chamber 13 is lowered, external air may flow backward into the cooling chamber 13 through the exhaust pipe 131. Therefore, the intake valve 91a is opened to the maximum extent, so that a large amount of ambient gas is continuously supplied into the heating chamber 12, thereby increasing the internal pressure of the heating chamber 12 and the cooling chamber. With the result that the backward flow of external air along the exhaust pipe 131 is prevented, and even if the internal pressure of the heating chamber 12 and the cooling chamber 13 are instantaneously decreased, the decreased internal pressure can be restored to normal pressure in a short period of time.
Therefore, the conventional heat treatment apparatus has problems in that consumption of the ambient gas is drastically increased, and the operational cost is correspondingly increased.
In addition thereto, when a workpiece 1, which is in a cooled state, is introduced into the heating chamber 12 or a heated workpiece 1 is rapidly cooled by the cooling unit, the internal temperature of the heating chamber 12 and the cooling chamber 13 are rapidly lowered and the internal pressure is also rapidly decreased due to the lowered temperature. At this point, since the ambient gas supply unit supplies a constant amount of ambient gas in a continuous manner, there is a limit to how quickly the lowered internal pressure can be restored to normal pressure. For this reason, external air is introduced into the chambers, thus causing the composition of the ambient gas to be unsteady. As a result, there are undesirable problems in that it is difficult to secure heat-treated products having a good quality, and explosion accidents may occur when the mixing ratio of ambient gas and air reaches the explosion region of the mixture.
Further, there are additional problems in which, since a large amount of ambient gas is used, additional costs are incurred in order to burn the ambient gas which is discharged outside, and the combustion of the ambient gas induces the generation of a large amount of carbon dioxide gas, thus causing environmental contamination.